Method for the production of acrylamide crystals

ABSTRACT

A method for the production of acrylamide crystals, characterized in preparing acrylamide crystals from an aqueous acrylamide solution, which contains at least one kind of surfactant selected from the group consisting of a cellulose glycolic acid salt and polyoxyethylene alkyl amine- and polyoxyethylene alkyl amide-type surfactants. The resulting acrylamide crystals are of higher purity, having less susceptibility to being concreted.

United States Patent Okuno et al.

[ 51 May 30, 1972 METHOD FOR THE PRODUCTION OF ACRYLANIIDE CRYSTALSInventors: Kenzo Okuno, Tokyo; Takaharu ltagakl, Kitakyushu; YoshimasaIsogai, Tokyo; Kazuo Yoshida, Kitakyushu; Konosuke Fujiki, Kitakyushu;Katumi Odagawa, Kitakyushu, all of Japan Assignee: Mitsubishi ChemicalIndustries Limited,

Tokyo, Japan Filed: Sept. 25, 1970 Appl. No.: 75,692

Foreign Application Priority Data Oct. 8, 1969 Japan. ...44/80543 Oct.8, 1969 Japan. ..44/80544 Oct. 8, 1969 Japan ..44/80545 US. Cl...260/561 N Int. Cl ..C07c 103/00 Field of Search ..260/561 N [56]References Cited UNITED STATES PATENTS 2,186,976 1/1940 Junkmann et al.....260/561 3,499,879 3/1970 Kobayashi ..260/88.7

Primary Examiner-Lewis Gotts Assistant Examiner-Ethel G. LoveAttorney-Oblon, Fisher & Spivak [5 7] ABSTRACT 7 Claims, No DrawingsMETHOD FOR THE PRODUCTION OF ACRYLAMIDE CRYSTALS The invention relatesto a method for the production of acrylamide crystals and moreparticularly to a method for the preparation of acrylamide crystalshaving improved properties from an aqueous acrylamide solution.

Acrylamide is extensively used in industries, particularly as a rawmaterial from which flocculating agent or paperstrengthening agent isprepared.

The conventional method in prior art for the production of acrylamidecrystals comprises hydrating acrylonitrile by use of sulphuric acid ascatalyst to produce acrylamide sulphate, subjecting the resultingacrylamide sulphate to neutralization employing ammonia or alkali toform free acrylamide, and filtering the major portion of ammoniumsulphate or alkali sulphate resulting from the said neutralization in asuitable manner to obtain an acrylamide solution thereby from whichsolid acrylamide is prepared in the form of crystals to be dried forpractical uses.

Acrylamide crystals thus prepared by the conventional method normallyare in the form of small flake or a massive material consisting of smallflakes overlapping one another. Thus, the conventional method involvesdisadvantages as follows.

First of all, difficulty has been experienced in removing such sulphateas ammonium sulphate or alkali sulphate and organic impurities from themother liquor with the result that a massive material consisting oflaminar or flaky acrylamide crystals retains an appreciable amount ofthe mother liquor between individual flakes which cannot be completelyremoved even by means of a powerful centrifugal separator. Inconsequence, acrylamide crystals when supplied for practicalapplications have contained a substantial amount of impurities.

Secondly, the flaky crystals or the massive material consisting of suchcrystals overlapping one another is crumbly and friable, and whensubjected to filtration or drying following the crystallization step,the crystals are liable to split into small pieces or particles wherebymaking for concretion of the crystals under transportation or storage toa solid lump.

As acrylamide crystal belongs to the monoclinic crystal system of poorsymmetry and possesses a good affinity with water which serves assolvent in the crystallization of acrylamide, the form of acrylamidecrystals available in the past has been limited to that of small piecesor an agglomeration, re-

gardless of any set of crystallization conditions. Hence, acrylamidecrystals produced by the conventional method normally have beensubjected to additional treatments before employment which comprisepurification of the crystals through the medium of recrystallizationusing a solvent, washing and drying. Apparently, such treatments bringabout a reduced yield of acrylamide, while the requirement of solventnecessitates various installations for supply, recovery and purificationthereof, leading to a higher production cost of acrylamide crystals.

In an attempt to mitigate such disadvantages by improving the shape ofacrylamide crystals, it has been proposed to employ a small amount ofsurfactant in preparing aqueous acrylamide solution to thereby formacrylamide crystals of a prismatic shape through the medium ofcrystallization.

In fact, the crystals having a prismatic shape are rather readilyfiltered off from the mother liquor, while getting wet with the motherliquor to a less degree, so that acrylamide crystals having a lesscontent of impurities are obtained.

This, however, has been only a partial solution of the problems, and theconcretion problem has remained unsolved in that even with the prismaticshape, acrylamide crystal still tends to split into small pieces orparticles of a smaller diameter in the course of centrifugal separationand drying which follow crystallization step whereby giving rise toconcretion of crystals, unless the crystal takes a thick shape ratherthan slender one.

Accordingly, an object of the invention is to provide a method for theproduction of acrylamide crystals of higher purity in which extraneoussteps are dispensed with.

Another object of the invention is to provide a method for theproduction of acrylamide crystals which are difficult to concrete duringstorage or transportation.

These and other objectives of the invention are accomplished bycrystallizing acrylamide out of an aqueous medium, which contains atleast one kind of surfactant selected from the group consisting of acellulose glycolic acid salt and polyoxyethylene alkyl amine andpolyoxycthylene alkyl amide type surfactants.

We have discovered that in order to avoid such concretion, it is needfulfor acrylamide crystals to satisfy the three requirements mentioned asfollows, in addition to the possession of a stereoscopic or cubic shape.

1. The ratio of length to mean diameter is more than 1 to less than 3.

2. The mean diameter is more than 0.4 mm, preferably more than 1 mm.

3. The concretion index" of crystals is less than 5.

The concretion index" referred to in this specification was designed toestablish a criterion of susceptibility to being concreted which wasdetermined by the method as illustrated later.

The term length" means the lengthwise measurement of a crystal from endto end; and the term mean diameter" means the measurement of thediameter of a crystal in its cross section assumed as a circle forexample, mean diameter of 1 mm signifies that the cross-sectional areais equivalent to that of a circle having diameter of 1 mm.

The method for determining the concretion index comprises:

Acrylamide crystals were spread about 5 mm deep over the flat bottom ofa vat for vacuum drying at 40 C. for 1 hour, so that the acrylamidecrystals contained about 1 to 2 percent water; 200 g of the acrylamidecrystals were placed in a cylindrical vessel having a 75 mm diameter anda mm height, and said vessel was placed in a conventional desiccatoremploying concentrated sulphuric acid as drying agent; the compressionmoulding of the resulting acrylamide crystals was carried out at 30 C.by applying a 5 kg load thereon for 20 hours; and the resultingcylindrical moulding was burdened on the upper surface thereof having a75 mm diameter with a minimal, compressive load needed to break themoulding to thereby obtain a concretion index, which is equivalent tothe absolute value of said load in terms of kg.

The invention provides a method for the production of acrylamidecrystals which satisfy the aforesaid three requirements.

Even in the case where the major portion of crystals meets the threerequirements, normally crystals tend to concrete to form a solid lump,if crystals passing through a 100 mesh Tyler screen account for morethan 5 percent. Thus, it is desirable to provide crystals of uniformsize. This requirement is also met with our method.

No particular limitations are imposed upon the aqueous acrylamidesolution used for crystallization operation, which is carried out in thepresence of surfactant according to our invention. The aqueousacrylamide solution, which is prepared by a process comprising hydratingacrylonitrile by use of sulphuric acid as catalyst, neutralising theresulting hydrate with ammonia or alkali to form sulphate and thenremoving a major portion of the sulphate from the mother liquor may bedirectly used for the method of the invention, without being affectedeither by the sulphate or by reaction by-products as for examplenitrilotripropionamide and acrylic acid contained in the aqueoussolution. Further, the method of the invention is applicable to thepurification of acrylamide through the medium of recrystallization inwater.

The method of the invention may be carried out in various modes. In thebatch process a quantity of surfactant is added toan aqueous acrylamidesolution for dissolution and acrylamide is then crystallized out of thesolution, whereas in the continuous process a quantity of surfactant isadded to the reaction liquor at any one of stages preceding thecrystallization step, said quantity being such that a suitableconcentration of surfactant is reached when the crystallization iseffected. In the latter case where the mother liquor is allowed tocirculate through the reaction system, no fresh feed. of surfactant isneedful excepting for the compensation of a loss thereof incurred in thecirculation of the mother liquor.

Regarding the surfactants employed in our method, any one kind ofsurfactant selected from the group consisting of the aforesaid celluloseglycolic acid salt and polyoxyethylene alkyl amine and polyoxyethylenealkyl amide type surfactants may be used individually to yieldacrylarnide crystals having improved properties, which satisfy theaforesaid requirements. It will be noted, however, that theeffectiveness of individual surfactants is not necessarily the same butvaries with the type thereof. For example, generally cellulose glycolicacid salt has a strong tendency to increase the thickness of thecrystals.

We have discovered that five types of surfactants, that is,polyoxyethylene sorbitan alkyl ester, polyoxyethylene alkyl ester,polyoxyethylene alkyl ether, polypropyleneglycol polyethyleneglycolether and polypropyleneglycol type surfactants possess a strong tendencyto increase the length of acrylamide crystal, and that the employmentfor the crystallization of acrylamide of cellulose glycolic acid salttogether with at least one of said five types of surfactant results inacrylamide crystals of good quality.

Adequate effect may be produced by the employment of any one kind of theaforesaid surfactants in an amount corresponding to a concentration offrom 5 to 1,000 ppm, preferably from to 500 ppm in relation to aqueousacrylamide solution, said concentration being applied to each of two ormore types of surfactant employed in combination, if such is the case.

The shape of acrylamide crystals may be modified by altering the mutualproportion of two or more kinds of surfactants used in combination.

Preferably, anti-foaming agent such as silicone oil is employed incarrying out the process of the invention, since a surfactant is apt tofoam a solution.

The method of the invention is applicable to the crystallizationoperation which is carried out in various modes. The employment ofsurfactant does not impose any particular limitation on thecrystallization conditions such as temperature and concentration ofacrylamide, as compared with those in prior art. Whilst thecrystallization conditions are fixed by taking into consideration themethod for crystallization, the structure and scale of apparatusemployed for crystallization and the like, normally a temperature in therange 050 C and a con centration of acrylamide in the range 30-400 g per100 g of water are employed according to the invention.

The method according to the invention provides acrylamide crystalshaving clean faces, which are of rather large size and approximatelycubic. This characteristic feature afiords commercial advantages asfollows.

In the first place, as the crystals provided by the invention aredifficult to break when subjected to impact in the course of stepssubsequent to crystallization, concretion of crystals during storage ortransportation is reduced to a great extent.

Secondly, removal of mother liquor from the crystals is rendered easy tofacilitate filtration and drying and to reduce the content of motherliquor with the result that the crystals get rid of impurities wherebyimproving the quality.

Some examples of the invention are illustrated in which part" means partby weight.

In order to determine as to how far the acrylamide crystals tend toconcrete during storage, the crystals were examined by the heapedconcretion test which comprises drying acrylamide crystals at atemperature from 45 to 50 C for 30 minutes, packing 500 kg of thecrystals each into a number of cylindrical transport bag which were madeof rubber, having a 900 mm diameter and a 900 mm height, and provided onthe upper surface in the center with an opening adapted to be tightclosed and having a 700 mm diameter, and disposing the bags with theopening closed in two layers in a storage kept at a temperature 2030 Cand a humidity 80-85 percent for inspection of the crystals contained inbags of the lower layer which was made later on having regard toconcretion state.

EXAMPLE 1 An aqueous acrylamide solution was prepared from 900 parts ofacrylamide, 200 parts of ammonium sulphate, and 1,000 parts of water.0.08 parts of sodium cellulose glycolate manufactured and sold byDaiichi Kogyo Seiyaku Co., Ltd. under the trade-name CELLOGEN PR weredissolved into 400 parts of the said solution, which was seeded withacrylamide powder at 195 C. The solution was cooled to 175 C, andstirred for 1 hour to form a slurry. Crystals filtered off from saidslurry possessed a platelike, approximately cubic shape with a 1 mmlength and 1 mm lean diameter. The concretion index showed 4.0. Thecontent of mother liquor was 2.0 percent. A heaped concretion testindicated no occurrence of concretion of the crystals upon a 30 daysstorage.

COMPARATIVE EXANIPLE 2 Acrylamide crystals were prepared by followingthe same process as Example 1 excepting that no CELLOGEN PR wasemployed. The crystals were found flaky or in the form of agglomerationof flakes. The concretion index was 10 and the mother liquor content 10percent.

EXAMPLE 3 An aqueous acrylamide solution composed of 35 percentacrylamide, 12 percent ammonium sulphate, 3 percentnitrilotripropionarnide and 50 percent water was used in this example. Aquantity of polyoxyethylene alkyl amine (the pH value of a 0.5 percentaqueous solution was about 10.) manufactured and sold by Kao Soap Co.,Ltd. under the trade-name LEVENOL A CONC was added to said solution soas to indicate ppm in regard to said solution. The crystallization waseffected at 10 C by means of a vacuum crystallizer of the draft tubetype with the residence time of approximately 1 hour and supersaturationdegree of about 0.1 kg per cubic meter. When steady state was reachedthe resulting slurry was subjected to filtration for 5 minutes by meansof a centrifugal separator to give crystals. The crystals were uniformin size, and took a platelike shape having a length 2-2.5 mm and a meandiameter about 1 mm. The concretion index showed 3.0, and the motherliquor content was 1.8 percent. A heaped concretion test indicated noconcretion of the crystals stored for 30 days.

COMPARATIVE EXAMPLE 4 Crystallization was carried out by the sameprocess as Example 3 excepting that no LEVENOL A CONC was employed. Theresulting crystals were very small and flaky. A centrifugal filtrationeffected under the same conditions as Example 3 gave crystals whichcontained l0 percent mother liquor. The concretion index showed 10.

EXAlviPLE 5 An aqueous solution composed of 56 percent acrylarnide, 1percent ammonium sulphate and 43 percent water was prepared. A quantityof the LEVENOL A CONC was added to said solution so as to indicate 200ppm. Crystallization was carried out by means of the same crystallizeras Example 3 at 5 C with residence time of 2 hours and supersaturationdegree of 0.05 kg/m. When steady state was reached, the resulting slurrywas subjected to filtration for 5 minutes by means of a centrifugalseparator. The resulting acrylamide crystals were uniform in size,having a platelike shape with a length 2.5-3 and a mean diameter about 1mm. The concretion index showed 2.0, and the mother liquor content was1.6 percent. A heaped concretion test indicated no concretion of thecrystals stored for 30 days.

EXAMPLE 6 An aqueous acrylamide solution composed of 40 percentacrylamide, 13 percent ammonium sulphate, 1 percentnitrilotripropionamide and 46 percent water was used. A quantity ofpolyoxyethylene alkyl amide manufactured and sold by Nippon Oils andFats Co., Ltd. under the trade-name NYMID 200, the pH value of 0.5percent aqueous solution thereof being about 9, was added to thesolution so as to indicate 100 ppm in regard to said solution.Crystallization was efiected at 5 C by means of a draft tube typecrystallizer with residence time of 2 hours and supersaturation degreeof 0.05 kg/m. The resulting slurry was subjected to filtration for 5minutes by means of a centrifugal separator to give acrylamide crystals,which were uniform in size, having a prismatic shape with a length 2-3mm and a mean diameter about 1 mm. The concretion index was 2.5 and themother liquor content 1.8 percent. A heaped concretion test indicated noconcretion of the crystals stored 30 days.

EXAMPLE 7 400 parts of the same aqueous acrylamide solution as example lwere employed. 0.04 parts of the CELLOGEN PR and 0.04 pans ofpolyoxyethylene sorbitan mono-oleate manufactured and sold by Kao SoapCo., Ltd. under the trade-name EMASOL 4130 were added to said solutionto follow the same process as Example 1. The resulting acrylamidecrystals were uniform in size, having a granular shape with a diameterabout 1.5 mm. The concretion index showed 1.8, and the mother liquorcontent was 1.5 percent. A heaped concretion test indicated nooccurrence of concretion of crystals stored 30 days.

EXAMPLE 8 An aqueous acrylamide solution containing 38.9 percentacrylamide and 9.0 percent ammonium sulphate was prepared by a processcomprising hydrating acrylonitrile in the presence of sulphuric acidserving as catalyst and neutralizing the resulting liquor by use ofammonia to remove the crystallized ammonium sulphate. 400 parts of saidaqueous solution were used in this example. 0.05 parts of the CELLOGENPR and 0.05 parts of polyoxyethylene sorbitan mono-stearate manufacturedand sold by Daiichi Kogyo Seiyaku Co., Ltd. under the trade-name SOLGENTW 60 were added to the solution and cooled to C to obtain acrylamidecrystals thereby. The resulting acrylamide crystals assumed a prismaticshape with a length 3 mm and a mean diameter about 1.2 mm. Theconcretion index was 2.0 and the mother liquor content 1.5 percent. Aheaped concretion test indicated no occurrence of concretion of thecrystals stored 30 days.

EXAMPLE 9 The same aqueous acrylamide solution as Example 1 wasemployed. 0.05 parts of the CELLOGEN PR and 0.05 parts of thepolypropyleneglycol polyethyleneglycol ether manufactured and sold byNippon Oils and Fats Co., Ltd. under the trade-name PLONON 204 wereadded to 400 parts of the said solution to follow the same process asExample 1. The resulting acrylamide crystals were of substantiallyuniform size with a length 2 mm and a mean diameter about 1 mm,possessing a prismatic or platelike shape much like single crystal. Theconcretion index showed 3.0, and the mother liquor content was 1.8percent. No occurrence of concretion of the crystals stored 30 days wasconfirmed by a heaped concretion test.

EXAMPLE 10 The same aqueous acrylamide solution as example 8 wasemployed. 0.04 parts of the CELLOGEN PR and 0.04 parts ofpolyethyleneglycol oleyl ether manufactured and sold by Daiichi KogyoSeiyaku Co., Ltd. under the trade-name NOlGEN ET-120 were added to 400parts of said solution to follow the process of Example 8. The resultingacrylamide crystals were uniform in size with a length 2 mm and a meandiameter about 1.5 mm, having a prismatic shape with clean faces. Theconcretion index showed 1.8, and the mother liquor content was 1.3percent. No concretion of the crystals stored 30 days was confirmed by aheaped concretion test.

COMPARATIVE EXAlvflLE 1 1 Acrylamide crystals were prepared by followingthe same process as Example 10 without employment of the CEL- LOGEN PRand NOIGEN ET-l20. The resulting acrylamide crystals were found flaky,having a concretion index of 10. The mother liquor content was 10percent. A heaped concretion test indicated complete concretion of thecrystals stored 2 days.

COMPARATIVE EXAMPLE 12 The same process as example 10 was followed byemploying 0.08 parts of the NOIGEN ET-l20 in place of 0.04 parts of theCELLOGEN PR and 0.04 parts of the NOlGEN ET-l 20. The resultingacrylamide crystals possessed a prismatic shape with a length 3-4 mm anda mean diameter about 1 mm.

Heaped concretion tests indicated occurrence of two lumps having adiameter about 40 cm in 17 days of storage, and substantially completeconcretion in 30 days of storage.

EXAMPLE 1 3 0.04 parts of the CELLOGEN PR and 0.04 parts ofpolyoxyethylene oleyl ether manufactured and sold by Nippon Oils andFats Co., Ltd. under the trade-name NONlON E-220 were added to 400 partsof aqueous 55 percent acrylamide solution to follow the same process asExample 1. The resulting acrylamide crystals had a prismatic shape withclean faces and were uniform in size with a length approximately 1.5 mmand a mean diameter 1 mm. The concretion index showed 3.3, and themother liquor content was 2.0 percent. A heaped concretion testindicated no concretion of the crystals stored 30 days.

COMPARATIVE EXAMPLE 14 Acrylamide crystals were prepared by followingthe same process as example 13 without employing the CELLOGEN PR andNONlON E-220. The resulting acrylamide crystals were flaky, havingconcretion index of 10 and mother liquor content of 10 percent.

EXAMPLE l5 0.04 parts of the CELLOGEN PR and 0.04 parts ofpolyethyleneglycol mono-stearate manufactured and sold by Nippon Oilsand Fats Co., Ltd. under the trade-name NONlON S-lO were added to 400parts of the aqueous acrylamide solution of Example 1, and the processof Example 1 was followed. The resulting acrylamide crystals having aprismatic shape were uniform in size with a length 2-2.5 mm and a meandiameter approximately 1 mm. The concretion index showed 2.5, and themother liquor content was 1.8 percent. A heaped concretion testindicated no concretion of the crystals stored 30 days.

EXAMPLE 16 The same aqueous acrylamide solution as example 1 wasemployed. 0.04 parts of the CELLOGEN PR and 0.04 parts ofpolypropyleneglycol manufactured and sold by Daiichi Kogyo Seiyaku Co.,Ltd. under the trade-name ANTIFROTH F102 were added to 400 parts of thesaid solution to follow the same process as Example 1. The resultingacrylamide crystals were of substantially uniform size with a length 1.5mm and a mean diameter about 1.5 mm, possessing a platelike shape. Theconcretion index showed 1.8, and the mother liquor content was 1.5percent. A heaped concretion test indicated no concretion of thecrystals stored 30 days.

Various modes of carrying out the invention are contemplated as beingwithin the scope of the following claims particularly pointing out anddistinctly claiming the subject matter which is regarded as theinvention.

We claim:

1. A method for the production of acrylamide crystals, characterized inpreparing acrylamide crystals from an aqueous acrylamide solution, whichcontains at least one surfactant selected from the group consisting of acellulose glycolic acid salt and polyoxyethylene alkyl amine andpolyoxyethylene alkyl amide surfactants.

2. A method as claimed in claim 1, further characterized in that theaqueous acrylamide solution contains, in combination, a celluloseglycolic acid salt and at least one member selected from the groupconsisting of polyoxyethylene sorbitan alkyl ester, polyoxyethylenealkyl ester, polyoxyethylene alkyl ether, polypropyleneglycolpolyethyleneglycol ether, and polypropyleneglycol surfactants.

3. A method for the production of acrylamide crystals, characterized incrystallizing acrylamide out of an aqueous medium containing apolyoxyethylene alkyl amine surfactant with a concentration from 5 to1,000 ppm.

4. A method for the production of acrylamide crystals, characterized incrystallizing acrylamide out of an aqueous medium containing a celluloseglycolic acid salt and polyoxyethylene alkyl ether surfactant with aconcentration from 5 to 1,000 ppm, respectively.

5. A method for the production of acrylamide crystals, characterized incrystallizing acrylamide out of an aqueous medium containing a celluloseglycolic acid salt and polyoxyethylene sorbitan alkyl ester surfactantwith a concentration from 5 to 1,000 ppm, respectively.

6. A method as claimed in claim 1, in which the concentration of thesurfactant is in the range 5-1.000 ppm.

7. A method as claimed in claim 2 in which the respective concentrationsof two or more surfactants, including cellulose glycolic acid saltcontained in the aqueous acrylamide solution are in the range 51 ,000ppm.

2. A method as claimed in claim 1, further characterized in that theaqueous acrylamide solution contains, in combination, a celluloseglycolic acid salt and at least one member selected from the groupconsisting of polyoxyethylene sorbitan alkyl ester, polyoxyethylenealkyl ester, polyoxyethylene alkyl ether, polypropyleneglycolpolyethyleneglycol ether, and polypropyleneglycol surfactants.
 3. Amethod for the production of acrylamide crystals, characterized incrystallizing acrylamide out of an aqueous medium containing apolyoxyethylene alkyl amine surfactant with a concentration from 5 to1,000 ppm.
 4. A method for the production of acrylamide crystals,characterized in crystallizing acrylamide out of an aqueous mediumcontaining a cellulose glycolic acid salt and polyoxyethylene alkylether surfactant with a concentration from 5 to 1,000 ppm, respectively.5. A method for the production of acrylamide crystals, characterized incrystallizing acrylamide out of an aqueous medium containing a celluloseglycolic acid salt and polyoxyethylene sorbitan alkyl ester surfactantwith a concentration from 5 to 1,000 ppm, respectively.
 6. A method asclaimed in claim 1, in which the concentration of the surfactant is inthe range 5-1,000 ppm.
 7. A method as claimed in claim 2 in which therespective concentrations of two or more surfactants, includingcellulose glycolic acid salt contained in the aqueous acrylamidesolution are in the range 5-1,000 ppm.